1. Field of the Invention.
The present invention relates to a gasket for a field adaptable push-on joint and the joint produced by two sections of pipe or piping appurtenances such as valves, fittings, hydrants and the like, and the gasket.
2. Description of Related Art.
Sealing and restraining gaskets are generally known in the art for use in pipe joints. For example, U.S. Pat. No. 3,963,298 by Seiler discloses a gasket having a plurality of "unibody" metal inserts disposed around the circumference of an elastomeric gasket. In one embodiment in that patent, the radial outer surface of each insert is provided with a curved surface which mates with a corresponding curved surface provided on an annular bead extending radially inwardly from the interior wall of the socket or bell. The shapes of the mating surfaces of these elements creates a pivot axis about which the metal inserts will be permitted to pivot or rotate relative to the pipe sections. In this embodiment, the annular bead in the socket must therefore be of a specific shape corresponding to a specific shape of the radial outer surface of the metal inserts disposed in the gasket. An undesirable feature of such an embodiment is that a special, more complicated bell structure is required in order to provide the mating surface for the metal inserts and thus has a relatively high cost of manufacture and the application of the restraining gasket is limited to use with the specific associated bell configuration.
A second embodiment is disclosed in the above-identified Seiler patent. In this embodiment, the specially shaped annular bead is not employed in the bell. Instead a specifically sized semicircular groove is provided adjacent to the end shoulder of the bell section. The plurality of metal inserts employed in this embodiment are provided with curved, convex radial outer surfaces which have a curvature and size corresponding to the curvature and size of the semicircular groove. While the bell structure may be considered to be somewhat less complicated in this embodiment, the ability of the metal inserts to securely grip and retain the inserted spigot end of the pipe continues to depend on the corresponding curvatures of the inserts and the semicircular groove in the bell, and the ability of the metal inserts to pivot within the groove. Thus, this embodiment also leaves much to be desired in terms of the cost of manufacture and the ability to use the gasket with other internal bell configurations.
U.S. Pat. No. 4,229,026, also issued to Seiler, discloses a further embodiment of a "unibody" metal insert adapted to be used as a gripping member in a rubber gasket. In this patent, the metal insert retaining elements are, on one hand, described as being fixedly embedded in the elastomer seal ring, while at the same time are described as being slidable as well as axially tiltable with respect to the elastomer parts of the ring. This movement of the retaining elements is possible only if the elastomeric material immediately adjacent the retaining elements also deforms to some extent to accommodate such movement.
In each of the embodiments disclosed in the '026 patent, the metallic retaining elements are tiltably supported on an annular bead extending radially inwardly from the inner wall of the bell. Several different shapes are proposed for the annular bead and the radial outer surface of the retaining elements. While the embodiments in this patent do not require the annular bead and retaining element to have identical curvatures for establishing a fixed pivot axis, there is an interdependence between the profiles of the annular bead and retaining elements. The retaining elements must remain in contact with the spigot end of the pipe, while at the same time being allowed to slide and tilt axially with respect to the elastomeric gasket. The specification notes that increasing retaining forces are generated by way of the retaining elements being driven in a wedge-like manner in the gap between the contact surface of the socket (annular bead) and the circumferential surface of the spigot end of the pipe. Thus, there is still a requirement to provide an internal bell configuration having a specially designed annular bead or profile which can increase the cost of manufacture and will affect the ability to use the gasket with other bell configurations.
In other pipe joints known in the art, separate means are employed to provide the sealing and retention functions. Assembling pipe joints of the bell-and-spigot type using separate sealing and retention means tends to be time consuming and costly. These type of joints further have generally not heretofore been self-actuating, thereby causing additional work be performed in the field in order to actuate the retention or restraining means.
It is therefore a principal object of the present invention to provide a gasket suitable for use in a push-on restrained joint which is less dependent on the particular internal bell configuration for effective operation in a field-adaptable bell-and-spigot joint.
It is another important object of the present invention to provide a gasket and a bell-and-spigot joint employing the gasket in which improved restraining forces are provided by restraining means disposed in the gasket.
It is another important object of the present invention to provide a gasket and a bell-and-spigot joint employing said gasket therein restraining means and disposed in the gasket which provide a substantially constant restraining force at any given pressure thrust level, regardless of the fit of the joint.
It is another object of the invention to provide pipe-restraining means embedded in the gasket which permit the elastomeric gasket to be made in either a single durometer or a dual durometer configuration.